Conventionally, in a vehicle provided with an internal combustion engine, an evaporated-gas purge system is used to prevent from discharging an evaporated gas generated in a fuel tank to the atmosphere. In the evaporated-gas purge system, the evaporated gas generated in the fuel tank is adsorbed in a canister, and a purge valve provided in a purge passage communicating with the canister and an intake system of the internal combustion engine is open. Therefore, the evaporated gas adsorbed at the canister is purged to the intake system according to a negative pressure of the intake system. The negative pressure corresponds to an intake negative-pressure. It is necessary to detect a leakage of the evaporated gas in an early stage to prevent from leaving a leakage state of the evaporated gas purged from the evaporated-gas purge system to the atmosphere.
JP-2003-269265A (US 2003/0131655A1) discloses a technology of detecting a leakage of an evaporation system from a fuel tank to a purge valve. Specifically, a leakage-checking module including a pressure sensor, an air pump, a reference-pressure detecting portion including a reference hole, and a passage-switching valve is connected to a canister of an evaporated-gas purge system. After the air pump introduces a pressure into the reference-pressure detecting portion to detect a reference pressure correlative to the reference hole, a pressure introducing passage is switched by utilizing the passage-switching valve, the pressure is introduced into the evaporation system of when the purge valve is closed and then the pressure in the evaporation system is detected, and a leakage abnormality is determined by comparing the reference pressure and the pressure in the evaporation system. When a negative pressure is introduced into the reference-pressure detecting portion and the reference pressure is lower than the pressure in the evaporation system, the leakage abnormality is determined to be generated. When the purge valve is controlled to be open and the pressure in the evaporation system is not increased after the pressure in the evaporation system is detected, a fixed closed abnormality of the purge valve in which the purge valve is fixed to be closed is determined.